Brazing two metal parts together such as two tubes, one telescoped inside the other, is accomplished by heating the area of the joint between the two tubes usually by ignition of a gas/oxygen mixture and introducing a braze alloy to the area to be joined, causing the alloy to melt and form around the area to be joined. With removal of the heat the alloy will solidify and seal the joint between the two tubes. Such brazing processes have been used particularly in sealing metal tubes such as copper to copper or copper to steel in hermetic sealed refrigerant systems used in refrigerators and air conditioners. Because the refrigerant system is to be hermetically sealed, each of the joints must be leakproof, which requires a high quality brazing operation. A good brazed joint is usually leakproof if the temperature of the two tubes to be joined together have been sufficiently heated to adequately melt and distribute the braze alloy around the joint area. On the otherhand, the two tubes should not be overheated to the extent that parent metal of the tubes may be burnt off. The result of overheating is degradation of the tubes in the area of the joint as they become brittle and in subsequent usage these tubes are frequently bent and if the tubes are too brittle, then they will crack and produce a leak.
In providing an automated brazing operation to join two metal parts together at a joint with a braze alloy, such as two metal tubes, one telescoped inside the other, there are two major failure modes associated with producing a good leakproof joint, namely, the joint is too cool to adequately melt and distribute the alloy around the joint or the joint is overheated resulting in degradation of the parts in the area of the joint. These failures can be caused by variations in temperature of the joint area due to variation in part mass and location, the quality and density of the gas being used to heat the joint, the improper mixture of the gas and oxygen to produce the flame, ambient temperature, and natural convection that occurs around the parts to be joined. Therefore, in automating a brazing operation it is important to control the temperature of the joint area as much as possible. In addition, it is advantageous to have a short cycle time for the braze operation so that production quantities can be increased without additional brazing equipment being needed.
By this invention there is provided an automated method of brazing to join two metal parts together at a joint with a braze alloy that produces a good joint by having adequate heat to melt and distribute the braze alloy around the joint but not too high a heat that would detrimentally affect the two parts being joined together and the process has a short cycle time per brazed joint.